Retractable undercarriage for airplanes and the like



R. L. .LEVY

Filed July :51. 1939 RETRACTABLE UNDERCARRIAGE FOR AIPLANES AND THE LIKESept. 8, 1942.

-,frm/Langa conditions-of retraction and said device is mainly'characterized by the fact that the chamber- Patented vSept. 8, 1942azimutsl RETRACTABLE UNDEMARIAGE For.: wAIRPLANES AND Tm: LIKE RenLucien Levy, Montrouge, France, assignor to Socit dlnventionsAronautiqueset Mcaniques, S. I. A. M., Fribourg, SvgitzerlarjApplication Julyl 31, 1939, Serial No. 287,635

In France July 26, 1938' 2 Claims. (Cl. 244-102) The present inventionrelates to a landing gear for an airplane.

In certain types of airplanes provided with a retractable undercarriage,it is necessary, in order to lodge the retracted undercarriage in theairretractable plane, for the length of said undercarriage, be-

tween the pivotal axis gud the wheels, to be more reduced in theretracted positionthan in the extended position. f

One solution of this problem, for 7undeicarriages in which thesuspension device forms part of the retractable system, consists inconnecting III about the pivot 2, for 'example in the direction -shownby thearrow f. The pivot pin 2 is xed to a suitable part of an airplaneshown generally at 30. .The shock-absorber comprises a cylinder 3 havinga piston 4 which isprovided with a constantly open narrow orice 5 andwith a valve 6 ythat ismovable opposite other'oriilces l which". Aarethus closed or opened according to whether the piston moves in thedirection of the arrow f1 or f2.

The piston 4 is provided with a hollow rod 8 by means of which it isrigidly connected to the the movable element of this shock-absorbing de-V vice to a xed point of the airplane by a connection of fixed length,such as a cable, rso that `the lifting of the undercarriage causes theretraction of the shock-absorber and, consequently, the desired decreaseof length.

Such a method of control must however be compatible with the structureof the suspension deviceinasmuch as this reduction of length must not begreater than the 4maximum retraction that can be supported by the.shock-absorber and must not require ank excessive expenditure of energyfor effecting it.

The present invention has for its object to provide al device whichfullls these particular which, in the shock-absorber, contains theliquid that reacts during the compression stroke, is connected to areceptacle by a pipe provided with a valve which is normally closed andthe opening of which is eected either by the pilot, or automatically. Inthis latter method of control; it is possible, optionally, `to use thehydraulic pressure that is used for the retraction.

The receptacle which receives the liquid forced back by the retractionof the undercarriage during the lifting may be open to the atmosphere,or on the contrary may form a closed air bell.'

The invention relates, in particular, to undercarriages having anoleo-pneumatic suspension device of the so-called two liquid'type, ifthis designation is applied to shock-absorbers in which the piston ismovable between two liquid layers bathing each of its faces, one 4ofsaid layers acting to brake the movement of the piston duringI thecompression stroke, the other during the ex-v pansion stroke.

The invention is illustrated in the accompanying drawing wherein thesingle ligure is an elevational view partly in section.

For the retraction, the wheel I carried by the wheel and relatively towhich the cylinder 3 can slide in a fluid-tight manner owing to thepresence of appropriate Dackings 9, an annular'space I0 between the lledwith liquid being thus provided hollow rod 8 and the cylinder.

- In the hollow rod 8, compressed air is initially introduced at apredetermined pressure through an'iniation orifice II. A floating pistonI2 separates this compressed air cushion from the liquid I3 locatedabove said piston in the upper compart- .ment of the cylinder.

strut forming a shock-absorbei` pivots with same The liquid contained inthe annular space I0 communicates, through a hose Il provided with avalve I5, with an air bell I6.

The valve I5 is such that it readily allowsthe liquid to pass in'thedirection of the arrow f3, but only oiers a narrow orifice for thecirculation in the opposite direction.

According to the invention the upper part of the cylinder 3 is connectedby a pipe I1 to a valve box I8. The valve box I8 is provided with achamber in which a, v alve I8 is arranged. The valve I9 is-yieldablyurged to a closed position on a seat 2| by means of a spring 20. A stem22 of the valve is adapted to be engaged by a iloating pis-I .thcylinder 3 and the hollow rod 8 normally per- `forms the function of ashock-absorber, so long as the pump 26 is not operating.

Under these conditions the compression stroke of the shock-absorberoccurs when the piston 4 moves in the direction of the arrow f1.. .Theliquid which is forced by the piston into the upper compartment, canonly escape through the orlce 5 and pushes the piston I2 downwards,increasing the pressure of the compressed air contained in the chamber8B.

At the same time, the liquid I5* of the bell has free access through thevalve I5 to illl the annular space I as the volume of said spaceincreases.

During the vexpansion stroke, the piston 4 moves in the direction of thearrow f,- the liquid contained in the space I0 is forced through thenarrow oriiice of the valve I5 into the bell Il, while the liquidlocated immediately above the piston I2 flows freely back into the uppercompartment of the cylinder 3, through the orice 5 and the o'riiices Iuncovered by the valve 6.

It will therefore be seen thatvthe narrow oril iice 5 for thecompression stroke, and the orifice of the valve I5 for the expansionstroke, ensure the hydraulic braking of the shocks lreceived by theshock-'absorber during travel along the ground, whereas the resilientsuspension is ensured by the pneumatic chamber 8".

During the retraction, the pump 25 having been started, the valve I9 ispushed back by the piston 23 and opens. At the same time, the liquiddelivered by the pump actuates, through the pipe 21a, the driving jackfor the retraction,

so that the strut formed of the members 3 and I pivots about the pin 2.

As the piston rod 8 is connected by a cable '28 to a suitably locatedxed point 29 of the airplane, said rod is urged, during this retractingmovement, to enter the cylinder 3 and move in the direction of the arrowf1 within said cylinder.

Without the valve box I8, this retraction of the shock-absorber would bebraked by the normal operation of same and the consequent compression inthe chamber 8'* might attain a magnitude incompatible with the poweravailable for effecting the retraction.

The invention eliminates these drawbacks by the opening of the valve I9which is immediately brought about by the starting of the pump 2G, sothat the liquid forced by the piston 4 into the pipe I1 can pass throughthe open valve ls and through the pipe z5, and be stored in the base ofthe bell I6. A part of the liquid thus delivered compensates for theincrease of volume of the annular space I0 during this movement of thepiston 4. However, since the volume of the liquid delivered by thepiston 4 is greater than' the increase of volume of the space I0, thepressure consequently increases in the bell I6.

The volume oi' said bell will be chosen sufilciently large for thepressure, after retraction, to remain still very low.

During the retraction of the undercarriage, the piston I2 does not movein the hollow rod 8, the pressure at 8 being very much greater than theresistances encountered by the liquid I3 forced towards the valve boxand the bell.

In the retracted position, the undercarriage is held by the pressureproduced in the pipes 25* and 21 which acts on the retracting jack ofsaid undercarriage.

However, the pressure that prevails above the liquid IIia actsdifferentially on the piston 4, since the stress which corresponds tosaid pressure is greater on the upper face of the piston 4 than on theperipheral ring corresponding to the annular space I0 on the oppositeface.

'Ihe pressure that prevails in the bell I6 therefore tends to drive thepiston 4 out of the shockabsorber and, consequently, to' cause theundercarriage to be lowered byl reaction on the cable 2l.

This reaction which effects the lowering only exists, in the retractedposition, if the cable 28 during its movement constantly remains below aline extending through the iixed pivots 2 and 29.

In order to lower the undercarriage, the pipes 25'l and 21* are placedin direct communication with the tank 21 by means of a valve 32. Theundercarriage is then no longer held and begins to` move downwards.During this downward movement, the liquid I6 which passes through thevalve I9 returns at I3 into the upper chamber of the shock-absorbercylinder.

Finally, all the liquid which was driven into the bell I6 during theprevious retraction, ilows through the pipes 25 and I1 and graduallyillls said chamber until the shock-absorber piston 4 reaches the end ofits outward stroke.

I claim:

1. In a retractable undercarriage for an airplane having a retractingmechanism, a landing member, a telescopic shock absorber for saidlanding member, a pivot for connecting the shock absorber to theairplane whereby the shock absorber may turn on the pivot to swing thelanding member to a retracted position, a linkage secured to theairplane and the shock absorber for decreasing the length of the shockabsorber during the retraction of the landing member, a piston in saidshock absorber providing a chamber on each side thereof, an auxiliarycontainer, a pipe connecting one chamber of the shock absorber withsaid'container, a normally closed valve interposed in said pipe when.the shock absorber is in a landing position, a pipe connecting saidauxiliary container with the other chamber of said shock absorber, apump for retracting the landing member, and means for opening said valveat the instant when the shock absorber starts to swing to a retractedposition.

2. In a retractable undercarriage for an airplane having a retractingmechanism, a landing member, a telescopic shock absorber for saidlanding member, a pivot for connecting the shock absorber to theairplane whereby the shock absorber may turn on the pivot to swing thelanding member to a retracted position, a linkage secured tothe airplaneand the shock absorber for decreasing the length of the shock absorber iof the shock absorber, a pump for retracting the landing member, andmeans movable upon starting of the pump for opening said valve,

- REN LUCIEN LEVY.

